1. Field of the Invention.
The invention relates to the mixing of materials such as foods and particularly to foods which are shear sensitive, thereby to prevent damage to the foods and to maintain the organoleptic and visual qualities of the food.
2. Description of the Prior Art.
Large scale cooking of food such as is necessary in an institutional situation and the like has long been accomplished in large cooking kettles, cooking or heating of foodstuffs in such kettles often requiring stirring or mixing operations which occur while the foodstuffs are being heated or cooked. Since mixing or stirring by hand is unreasonably laborious even in the smaller kettles used in hotels, restaurants, health care facilities and the like, the use of power driven mixers has long been known. Such mixers often take the form of structural elements which merely stir a food or other material which is to be mixed either with or without cooking or heating. Conventional mixing agitators also exist which not only mix food materials being cooked or heated in a kettle, but also scrape the surfaces of the kettle which contact the food materials to prevent the sticking of overheated food materials to surfaces of the kettle which can occur due to localized overheating of the food materials which simple stirring often cannot prevent. Accordingly, mixing agitators having scraper elements which contact food-contacting surfaces of cooking kettles have previously been provided in the art, such mixers acting not only to scrape the walls of the kettle to displace food materials positioned adjacent the walls but which also act to mix and blend the remaining portions of the body of the food materials.
Mixing agitators having scraping capability are disclosed by Groen, Jr. in U.S. Pat. No. 3,752,057, this patent describing a mixer having a shaft which extends into a kettle at an angle of at least 20.degree. with respect to the vertical axis of the kettle. The shaft of Groen, Jr. is provided with a hoop-like structure at the distal end of the shaft, the hoop-like structure having a plurality of scrapers pivotally mounted to said structure at differing inclinations to the axis of the shaft, the scrapers acting to contact surface portions of the kettle in order to prevent food "burn-on" when a food material is being heated within a cooking kettle.
Giusti, in U.S. Pat. No. 4,199,266, describes a mixing agitator having a scraping capability wherein a rotary shaft is disposed horizontally within a cooking kettle, the shaft having a substantially circular agitator mounted thereon and wherein the agitator is formed of a pair of substantially annular semicircular blades each having an internal segment-shaped web. The annular blades each carry a plurality of scrapers at their respective periperhies for scraping of internal surfaces of a kettle.
Both the Groen, Jr. and Giusti patents act to move cooking foods from the bottom of the kettle at which location the greatest amount of heat is being directed into the cooking material and lift the food material to the vicinity of the upper most portion of the body of the food material, thereby giving that food material near the top of the kettle a chance to flow downwardly and into contact with the heated surfaces of the kettle at the bottom of the kettle. A mixing and blending of the material thus occurs with the scraping of the walls of the kettle being intended to assure that no portion of the food material remains near the cooking surfaces for a time sufficient to cause overheating of portions of the food material.
Examples of other mixing agitators, some of which include scraping elements, are disclosed by Rebechini in U.S. Pat. No. 2,753,158; Hirshon in U.S. Pat. No. 2,580,780; Costa et al in U.S. Pat. No. 3,739,710; and Addision in U.S. Pat. No. 3,731,339. With the exception of the Costa et al patent, the mixers described above do not employ agitators having a vertical axis since such vertical axis agitators must function at high speed to effectively mix certain foods which consist of solid pieces in a liquid base. Operation of such mixers at high speed exerts a substantial shearing effect on the solid materials in such a mixture, thereby resulting in fragmentation and damage to such solid pieces when the solid pieces are of a shear sensitive nature. Accordingly, in many food mixing situations, mixing at a low speed is necessary in order to prevent physical degradation of the food. A gentle lifting of food materials near the bottom of a cooking kettle is thus required in order to prevent damage to shear sensitive food materials in a mixture which is either being simply mixed or mixed during a cooking or heating process. While mixing agitators having a scraping capability have been previously utilized in the art as indicated above, such mixing agitators have been intended to be "universal" in operation, that is, the prior agitators have been intended to be useful in a wide range of applications as diverse as food processing, chemical processing, cosmetics mixing, pharmaceutical processing and the like. The mixing requirements of these diverse applications can be quite different. Accordingly, agitator structures designed to function in a number of these various applications typically are not well adapted for optimum usage in all of the different applications and may only be barely adequate for any specific mixing application. The present mixing agitator and scraper assembly is primarily designed for use in food processing and is intended for use in the mixing of foods which are being cooked or heated in a kettle such as a steam-jacketed kettle with the foods either having a water base or roux base with thickeners. The scraping capability of the present mixing agitator is particularly necessary for the roux-base materials to prevent "burn-on" during cooking. While the present mixing agitator can be employed in fields other than food processing with performance at least equal to most commercially available agitators, the present mixing agitator finds particular utility in the food processing field and allows extremely thorough and gentle mixing of food materials including scraping of the containing kettle. The present agitator and scraper assembly is a relatively simple and inexpensive structure which can be rapidly assembled and disassembled without the use of tools, thus facilitating cleaning of the agitator and kettle and reducing the time required between cooking of different materials within the same kettle. Accordingly, the present invention provides a mixing agitator having a scraping capability and which provides performance, operational and cost advantages over agitators of the prior art.